Production method of 4,6-diaminoresorcin

ABSTRACT

The present invention relates to a novel production method of 4,6-diaminoresorcin, and to 2-sulfonic acid-4,6-dinitroresorcin as its intermediate and salts thereof. The target compound is obtained by (R1) sulfonating resorcin (A) to obtain resorcin 2,4,6-trisulfonate (B), (R2) nitrating the compound (B) to obtain 2-sulfonic acid-4,6-dinitroresorcin (C), (R3) hydrolyzing the compound (C) to obtain 4,6-dinitroresorcin (D), and finally (R4) reducing the compound (D) to obtain 4,6-diaminoresorcin (E):

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a novel production method of4,6-diaminoresorcin which is a monomer for polybenzobisoxazole (PBO).More particularly, it relates to a production method of4,6-diaminoresorcin in which resorcin is-used as a starting material,any step of forming a halogen-containing compound is not required andthe production of by-products is inhibited. Furthermore, the presentinvention relates also to a novel intermediate useful for the synthesisof 4,6-diaminoresorcin and a production method of this intermediate.

[0003] A PBO fiber is superior to conventional fibers in terms ofvarious properties such as strength, modulus of elasticity, heatresistance and chemical resistance, as disclosed in Japanese PatentPublication No. 501452/1986, so that it is expected to apply this kindof fiber to various uses including structural materials and thermalinsulating materials as a super fiber which is superior to aramid, andhence the fiber is considered to be an industrially extremely usefulresin. 4,6-Diaminoresorcin is a monomer for the PBO, and therefore, itis important as a raw material for the PBO.

[0004] 2. Description of the Related Art

[0005] A PBO is a polymer represented by the following generalstructural formula (c) and can be obtained through a condensationreaction between a compound (a) and a compound (b) as represented by thefollowing reaction formula:

[0006] wherein Ar is an aromatic group; and Y is a functional grouphaving an electron-deficient carbon such as a carboxyl group, acarboxylic acid halide group, a haloalkyl group or a nitrile group.

[0007] The thus obtained polybenzobisoxazole is used as fibers, filmsand the like, but its physical properties such as strength and modulusof elasticity are greatly influenced by a polymerization degree of thepolymer. It is known that in a polycondensation reaction, a maximumpolymer viscosity is generally obtained when a feed ratio of themonomers is 1:1, and the polymer viscosity rapidly decreases as the feedratio of the monomers deviates from a ratio of 1:1. That is, to attain asatisfactory sufficient polymerization degree, it is necessary tostrictly control the feed ratio of the monomers.

[0008] However, in the case that the monomers contain impurities inlarge quantities, it is difficult to control this feed ratio of themonomers. Particularly, when the monomers contain even small amounts ofmonoamine and triamines which act as polymerization terminators, thedeterioration of the polymerization degree is caused. Therefore, therehave been desired the high-purity monomers containing neither themonoamine nor the triamines.

[0009] As a monomer (a) for the PBO, 4,6-diaminoresorcin is known, andseveral synthesis methods for this compound have been reported.

[0010] A conventional production method of 4,6-diaminoresorcin comprisessynthesizing dinitroresorcin as a precursor by a method in whichresorcin is acetylated and then nitrated (Ber. Dtsch. Chem. Ges., 16,552, 1883), a method in which 1,3-bis(alkyl carbonate)benzene isnitrated (Japanese Patent Application Laid-Open No. 136/1990) or anothermethod, and then reducing the thus synthesized dinitroresorcin.

[0011] However, the operation of this conventional method is complicatedand a manufacturing cost increases, because protecting groups areintroduced for the hydroxy groups of resorcin, and from an industrialviewpoint, the above method has a problem that the protecting groupseliminated in a hydrolysis step become an unrecoverable by-product, anda problem that a trinitro compound is produced in the nitration step anda triamino compound is produced in the reduction step, and they disturbthe polymerization in the synthesis of the PBO.

[0012] Furthermore, several methods using no protecting groups have beenproposed in which a halobenzene is used as a raw material, and there areknown, for example, a method in which a trichlorobenzene is nitrated(Japanese Patent Application Laid-Open No. 500743/1990) and a method inwhich a dihalobenzene is nitrated and then hydrolyzed with an alkali(Japanese Patent Application Laid-Open Nos. 238561/1989, 233127/1995,316102/1995 and 73417/1996).

[0013] In these methods, however, since 4,6-dinitro-resorcin is unstableunder the alkali conditions in the hydrolysis step, the operation ofthese methods is apt to be complicated in order to avoid thedecomposition of produced 4,6-dinitroresorcin. Furthermore,trichlorobenzene and its nitrated compound have a problem that they arestrongly poisonous and cause an irritation on skin. Therefore, it is notpreferable in consideration of the safety of an operator to pass throughthe production of a halogen-containing compound such as the halobenzeneand its nitrated compound.

[0014] In addition, another method which comprises subjecting an anilineto diazotization and diazo-coupling the thus diazotized compound toresorcin, followed by hydrocracking is disclosed in Japanese PatentApplication Laid-Open Nos. 242604/1995 and 124575/1997. In this method,however, aniline produced by the hydrocracking might be mixed with theproduct, and might disturb the polymerization in the synthesis of thePBO.

SUMMARY OF THE INVENTION

[0015] It is an object of the present invention to provide a novelproduction method of 4,6-diaminoresorcin in which any step of forming ahalogen-containing compound is not required and the production ofby-products is inhibited.

[0016] It is another object of the present invention to providea-production method of 4,6-dinitroresorcin, as a precursor of4,6-diaminoresorcin, via the production of a novel intermediate.

[0017] It is still another object of the present invention to provide aproduction method of a high-molecular-weight PBO by the use ofhigh-purity 4,6-diaminoresorcin obtained by these methods.

[0018] The present inventors have made intensive studies to solve theabove problems, and found that 4,6-diaminoresorcin can be obtained at ahigh yield by sulfonating resorcin to form resorcin 2,4,6-trisulfonate,nitrating resorcin 2,4,6-trisulfonate to obtain 2-sulfonicacid-4,6-dinitroresorcin with a high position selectivity, hydrolyzingthis compound to form 4,6-dinitroresorcin, and then reducing the same.In consequence, the present invention has been attained.

[0019] Furthermore, the present inventors have found that ahigh-molecular-weight PBO can be obtained by hydrolyzing 2-sulfonicacid-4,6-dinitroresorcin to obtain 4,6-dinitroresorcin containingneither isomers nor trinitro compounds, reducing this compound to obtainhigh-purity 4,6-diaminoresorcin, and then polymerizing the same. Thus,the present invention has been achieved.

[0020] That is, the present invention includes the following aspects.

[0021] 1. A production method of resorcin 2,4,6-trisulfonate whichcomprises the step of bringing resorcin into contact with a sulfonatingagent.

[0022] 2. The production method of resorcin 2,4,6-trisulfonate accordingto the above (1), wherein fuming sulfuric acid is used as thesulfonating agent.

[0023] 3. The production method of resorcin 2,4,6-trisulfonate accordingto the above (2), wherein fuming sulfuric acid to be used contains 3mols or more of free SO₃ per mol of resorcin.

[0024] 4. A production method of 2-sulfonic acid-4,6-dinitroresorcinwhich comprises the step of nitrating resorcin 2,4,6-trisulfonate.

[0025] 5. The production method of 2-sulfonic acid-4,6-dinitroresorcinaccording to the above (4), wherein the nitration is carried out insulfuric acid or a fuming sulfuric acid solvent.

[0026] 6. A production method of 2-sulfonic acid-4,6-dinitroresorcinwhich comprises the following steps:

[0027] (1) a first step of producing resorcin 2,4,6-trisulfonate bybringing resorcin into contact with a sulfonating agent, and

[0028] (2) a second step of producing 2-sulfonicacid-4,6-dinitroresorcin by bringing resorcin 2,4,6-trisulfonate intocontact with a nitrating agent.

[0029] 7. A production method of 4,6-dinitroresorcin which comprises thestep of hydrolyzing 2-sulfonic acid-4,6-dinitroresorcin.

[0030] 8. The production method of 4,6-dinitroresorcin according to theabove (7), wherein the hydrolysis is carried out in water or an aqueousmineral acid solution.

[0031] 9. The production method of 4,6-dinitroresorcin according to theabove (8), wherein sulfuric acid is used as the mineral acid.

[0032] 10. A production method of 4,6-dinitroresorcin which comprisesthe following steps:

[0033] (1) a first step of producing resorcin 2,4,6-trisulfonate bybringing resorcin into contact with a sulfonating agent,

[0034] (2) a second step of producing 2-sulfonicacid-4,6-dinitroresorcin by bringing resorcin 2,4,6-trisulfonate intocontact with a nitrating agent, and

[0035] (3) a third step of producing 4,6-dinitroresorcin by hydrolyzing2-sulfonic acid-4,6-dinitroresorcin.

[0036] 11. A production method of 4,6-diaminoresorcin which comprisesthe following steps:

[0037] (1) a first step of producing resorcin 2,4,6-trisulfonate bybringing resorcin into contact with a sulfonating agent,

[0038] (2) a second step of producing 2-sulfonicacid-4,6-dinitroresorcin by bringing resorcin 2,4,6-trisulfonate intocontact with a nitrating agent,

[0039] (3) a third step of producing 4,6-dinitroresorcin by hydrolyzing2-sulfonic acid-4,6-dinitroresorcin, and

[0040] (4) a fourth step of producing 4,6-diaminoresorcin by reducing4,6-dinitroresorcin.

[0041] 12. A production method of polybenzobisoxazole which comprisesthe steps of hydrolyzing 2-sulfonic acid-4,6-dinitroresorcin, followedby reducing to obtain 4,6-diaminoresorcin, and then reacting the thusobtained 4,6-diaminoresorcin with aromatic dicarboxylic acid.

[0042] 13. 2-Sulfonic acid-4,6-dinitroresorcin represented by thefollowing formula and salts thereof:

[0043] wherein M is hydrogen, an alkali metal or an alkaline earthmetal, and n is 1 or 2.

[0044] 14. A production method of 4,6-diaminoresorcin which comprises:

[0045] (1) a first step of producing 4,6-dinitroresorcin by hydrolyzing2-sulfonic acid-4,6-dinitroresorcin, and

[0046] (2) a second step of producing 4,6-diaminoresorcin by reducing4,6-dinitroresorcin.

[0047] 15. The production method of 4,6-diaminoresorcin according to theabove (14), wherein 2-sulfonic acid-4,6-dinitroresorcin is obtained bythe following steps:

[0048] (1) a first step of producing resorcin 2,4,6-trisulfonate bybringing resorcin into contact with a sulfonating agent, and

[0049] (2) a second step of producing 2-sulfonicacid-4,6-dinitroresorcin by bringing resorcin 2,4,6-trisulfonate intocontact with a nitrating agent.

[0050] 16. The production method of 4,6-diaminoresorcin according to theabove (14), wherein in the second step, 4,6-dinitroresorcin is reducedin an aqueous mineral acid solution.

[0051] 17. The production method of 4,6-diaminoresorcin according to theabove (16), wherein hydrochloric acid is used as the mineral acid.

[0052] 18. The production method of 4,6-diaminoresorcin according to theabove (14) which comprises the steps of dissolving or suspending4,6-dinitroresorcin in a solvent, adjusting the pH of the suspension ina range of 4 to 5 to obtain 4,6-dinitroresorcin, and then reducing thethus obtained 4,6-dinitroresorcin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] A production method of 4,6-diaminoresorcin of the presentinvention can be accomplished via the following intermediate compounds.

[0054] First, resorcin (i.e., 1,3-benzenediol) (A) as a raw material isbrought into contact with a sulfonating agent (reaction R1) to obtainresorcin 2,4,6-trisulfonate (B). Successively, sulfonic groups atpositions 4 and 6 are selectively nitrated (reaction R2) to obtain2-sulfonic acid-4,6-dinitroresorcin (C), which is then hydrolyzed(reaction R3) to obtain 4,6-dinitroresorcin (D). Finally,4,6-dinitroresorcin (D) is reduced (reaction R4) to obtain desired4,6-diaminoresorcin (E).

[0055] To produce resorcin 2,4,6-trisulfonate, as described inBerichite, 10, 182, there is known a method in which a disulfonic acidresorcin is heated at 200° C. in fuming sulfuric acid. However, in thecase that the thus formed disulfonic acid resorcin is isolated and thenused in the subsequent step, a process becomes complicated and theserious decrease of yield occurs. Thus, the above method has beenunsuitable for industrial practice.

[0056] Next, each of the reaction steps R1 to R4 will be described indetail hereinafter.

[0057] In the first reaction step R1, a sulfonating agent can be usedthat sulfonates resorcin (A) to produce resorcin 2,4,6-trisulfonate (B).Illustrative examples of the sulfonating agent include concentratedsulfuric acid, fuming sulfuric acid and sulfur trioxide. The reactionmay be carried out using an appropriate solvent. However, it isindustrially advantageous that the reaction is carried out in excessconcentrated sulfuric acid or fuming sulfuric acid without using asolvent. To avoid desulfonation caused by hydrolysis, concentratedsulfuric acid or fuming sulfuric acid is preferably used at aconcentration of 80 to 100% by weight, more preferably 95% by weight ormore. Above all, the use of fuming sulfuric acid is most preferable.

[0058] According to the investigation of the present inventors, theselectivity of resorcin 2,4,6-trisulfonate depend largely on theconcentration of SO₃in sulfuric acid. As the SO₃concentration insulfuric acid decreases, the selectivity of resorcin 2,4,6-trisulfonatedecreases. For example, even if 95 wt % sulfuric acid(SO₃concentration=77.6%) is used, the preparation of resorcin2,4,6-trisulfonate is possible, but it has been confirmed that in thecase that 95 wt % sulfuric acid (SO₃ concentration=77.6%) is used, theselectivity of resorcin 2,4,6-trisulfonate is in a range of about 12 to17 mol %, and remaining 83 to 88 mol % thereof is resorcin4,6-disulfonate. This fact can be considered to be due to the decreaseof the sulfuric acid concentration by water produced during thereaction. To attain such a yield as can be industrially satisfied, it isdesirable that the SO₃ concentration in sulfuric acid at the completionof the reaction is 81.6% or more, i.e., the sulfuric acid concentrationis about 100% or sulfuric acid contains an excessive amount of free SO₃.To maintain such a state, the sulfonation should be carried out by usingfuming sulfuric acid containing 3 mols or more of free SO₃ per mol ofresorcin.

[0059] The amount of the sulfonating agent to be used is notparticularly limited, as long as it satisfies the above SO₃concentration. It is, however, preferably 5 to 50 times more by weightthan resorcin in view of volumetric efficiency and efficient agitation.

[0060] To bring resorcin into contact with the sulfonating agent, one ofthem may be added to the other or vice versa.

[0061] As for a reaction temperature, the reaction may be carried outwithin any temperature range in which the desired product can beobtained. However, a temperature range of from about 0 to about 200° C.is preferable. To avoid the installation of large cooling facilitieswhich is required for heat generation at the time of the sulfonation,the reaction temperature is desirably 20° C. or higher. To prevent anundesirable side reaction, the reaction temperature is desirably 150° C.or lower.

[0062] Resorcin 2,4,6-trisulfonate can be isolated from a reaction massby adding dropwise the reaction mass to an aqueous solution of aninorganic salt such as sodium sulfate to cause salting-out, followed byfiltering and drying.

[0063] Next, reference will be made to the reaction step R2 in which2-sulfonic acid-4,6-dinitroresorcin (C) is obtained from resorcin2,4,6-trisulfonate (B). The reaction step R2 is a nitration step, inwhich a known nitrating agent capable of producing the desired compoundcan be used. Illustrative examples of the nitrating agent include nitricacid, fuming nitric acid, and nitrates such as sodium nitrate andpotassium nitrate. The nitration may be carried out after the isolationof resorcin 2,4,6-trisulfonate from the sulfonated reaction mass asdescribed above, but it is industrially advantageous that the nitrationis carried out in a one-pot manner by adding the nitrating agent to thesulfonated reaction mass (in this case, the nitration is carried out insulfuric acid or a fuming sulfuric acid solvent). The amount of thenitrating agent to be used is in a range of about 1 to 10 mols per molof resorcin (A) as a starting material, and in order to sufficientlypromote the reaction and to inhibit the excessive nitration, it ispreferably in a range of about 2 to 4 mols per mol of resorcin (A).

[0064] The reaction step R2 can also be carried out within anytemperature range in which the desired product can be obtained. However,when the reaction temperature is too high, the reaction proceedsquickly, whereby the undesirable side reaction may occur on occasion.Therefore, the reaction is usually carried out while the reactiontemperature is controlled by cooling. The reaction temperature ispreferably in a range of about 0 to 80° C., more preferably about 0 to50° C.

[0065] To isolate desired 2-sulfonic acid-4,6-dinitroresorcin (C) fromthe reaction mass after the completion of the reaction, the reactionmass is first neutralized with an alkali to form an alkali metal salt oran alkaline earth metal salt, which is then subjected to salting-out tothereby deposit the salt, so that the desired salt is obtained as amixture with an alkali metal salt or an alkaline earth metal salt ofsulfuric acid. In succesion, the mixture is added to, for example, amixed solution containing water and ethanol in a ratio of 2:8, and theresultant solution is then heated at 50 to 80° C. to dissolve thedesired compound. Afterward, the inorganic salt is removed by filtrationunder heating. The resultant filtrate is cooled to deposit yellowcrystals, which are then filtered to thereby obtain an alkali metal saltor an alkaline earth metal salt of 2-sulfonic acid-4,6-dinitroresorcin(C). Alternatively, the solvent may be removed from the filtrate toobtain the alkali metal salt or the alkaline earth metal salt of2-sulfonic acid-4,6-dinitroresorcin (C). The alkali metal salt or thealkaline earth metal salt can be desalted by dissolving the salt inwater, passing the solution through a column filled with a stronglyacidic cation exchange resin, and removing water therefrom. Inconsequence, 2-sulfonic acid-4,6-dinitroresorcin (C) is obtained.

[0066] Next, reference will be made to the reaction step R3 in which2-sulfonic acid-4,6-dinitroresorcin (C) is hydrolyzed to obtain4,6-dinitroresorcin (D).

[0067] The hydrolysis is carried out in water or an aqueous solutioncontaining an acid or an alkali as a catalyst. However, it is preferablycarried out in water or the acid-containing aqueous solution, morepreferably in a mineral acid-containing aqueous solution, because thereis a fear that 4,6-dinitroresorcin (D) after the hydrolysis may bringabout a further decomposition reaction in the alkali aqueous solutionhaving a high concentration. Examples of the mineral acid which can beused herein include sulfuric acid, hydrochloric acid and phosphoricacid. The mineral acid is preferably sufficiently diluted with water, ora sulfuric acid coupling agent may be added thereto in order to avoidthe recombination of the separated sulfonic group. In the hydrolysisstep R3, the concentration of the mineral acid is preferably in a rangeof 5 to 90% by weight, and in order to maintain a sufficient hydrolysisrate and to obtain a sufficient yield, it is desirably 10% by weight ormore. The amount of the aqueous mineral acid solution to be used is notparticularly limited, but it is preferably about 2 to 50 times by weightmore than 2-sulfonic acid-4,6-dinitroresorcin (C) in view of agitationefficiency and volumetric efficiency. The reaction temperature ispreferably in a range of from 50° C. to reflux temperature or so.

[0068] This hydrolysis step R3 may be carried out after 2-sulfonicacid-4,6-dinitroresorcin (C) has been isolated, or alternatively it maybe carried out without isolating 2-sulfonic acid-4,6-dinitroresorcin (C)from the reaction mass in the nitration step R2.

[0069] When the hydrolysis is directly carried out without isolating2-sulfonic acid-4,6-dinitroresorcin (C), the reaction mass in thenitration step R2 is diluted so as to become the aqueous mineral acidsolution which meets predetermined conditions. Furthermore, when2-sulfonic acid-4,6-dinitroresorcin is isolated as the alkali metal saltor the alkaline earth metal salt, the salt may be directly used as it isin the hydrolysis step. In addition, the salt may be used in the form ofa mixture with an alkali sulfate.

[0070] As the hydrolysis reaction proceeds, crystals of4,6-dinitroresorcin (D) are gradually deposited. Therefore, thesecrystals are filtered after the completion of the reaction to-obtain thedesired product. The thus obtained 4,6-dinitroresorcin (D) may bepurified as required prior to its use. The compound 4,6-dinitroresorcin(D) may be purified by subjecting it to sludging in or recrystallizationfrom a solvent such as ethanol. However, it is preferable for thepurpose of preventing the deterioration of a catalytic activity in thereduction step to dissolve or suspend 4,6-dinitroresorcin (D) in asolvent such that the resulting solution has a pH of 4 to 5. Concretely,any of the following procedures can be taken.

[0071] (1) An alkali is added to a solution or slurry in which4,6-dinitroresorcin is dissolved or suspended in a solvent, therebyadjusting the pH in a range of 4 to 5.

[0072] (2) 4,6-Dinitroresorcin is dissolved in a two-layer mixed solventof water and a hydrophobic solvent, and an alkali is then added to thesolution, thereby adjusting the pH in a range of 4 to 5.

[0073] (3) 4,6-Dinitroresorcin, which is in the form of an alkali salt,is dissolved in water, and an acid is then added to the solution,thereby adjusting the pH in a range of 4 to 5.

[0074] Examples of a hydrophilic solvent which is one type of thesolvent to be used include water, methanol, ethanol, n-propanol,iso-propanol, DMI (1,3-dimethyl-2-imidazolidinone) and DMF(N,N-dimethylformamide). Examples of a hydrophobic solvent which is theother type of the solvent to be used include ethyl acetate,1,3-dimethoxybenzene, phenetole and anisole. The amount of the solventdepends on the kind of solvent to be used, but it is in a range of 1 to100 times more than that of 4,6-dinitroresorcin. The above alkali is notparticularly limited, but its examples include potassium hydroxide,sodium hydroxide, potassium carbonate and sodium carbonate. The aboveacid is not particularly limited, but its examples include mineral acidsuch as hydrochloric acid and sulfuric acid. A temperature at the pHadjustment depends on the kind of solvent to be used, but it ispreferably in a range of 10 to 80°C.

[0075] The isolation of purified 4,6-dinitroresorcin, in the case thatthe pH adjustment is made in the slurry state, is carried out byfiltrating the slurry as it is, washing the collected substance with theused solvent, and further washing it with water. In the case that the pHadjustment is made in the two-layer heterogeneous state, the isolationis carried out by allowing the obtained solution to stand forseparation, washing the separated organic phase with water, cooling itfor crystallization, and then filtering the resultant crystals. In thecase that 4,6-Dinitroresorcin in the form of the alkali salt isdissolved and the acid is then added, the isolation is carried merely byfiltrating the obtained mixture as it is, and then washing it withwater.

[0076] Finally, reference will be made to the reduction step R4 in which4,6-diaminoresorcin (E) is obtained from 4,6-dinitroresorcin (D).

[0077] In this step, any reduction technique may be used as long as thedesired product is obtained. However, a catalytic reduction is usuallycarried out in the presence of a noble metal catalyst. The noble metalcatalyst to be used herein is a platinum group metal such as palladium,platinum, rhodium or ruthenium which is carried on a proper carrier, andit is preferable to use palladium or platinum carried on carbon.

[0078] The amount of the catalyst to be used is in a range of 0.1 to 10%by weight, preferably 0.5 to 5% by weight, based on 4,6-dinitroresorcin(D). A reaction temperature is in a range of 20 to 100° C., and ahydrogen pressure is in a range of 0.1 to 10 MPa.

[0079] The solvent usable in the reaction is water, an organic solvent,an organic acid, or a mixture of water and a mineral acid. Examples ofthe usable mineral acid include hydrochloric acid, phosphoric acid andsulfuric acid. Above all, the employment of hydrochloric acid ispreferable, because a hydrochloride of 4,6-diaminoresorcin is formedsimultaneously with the reduction of 4,6-dinitroresorcin and thishydrochloride is dissolved in water to form a homogeneous solution whichis easy to handle. Examples of the organic solvent include aromatichydrocarbons such as benzene and toluene, and alcohols such as methanoland ethanol. Examples of the organic acid include acetic acid andpropionic acid.

[0080] The formed 4,6-diaminoresorcin (E) is converted into a mineralacid salt to avoid oxidation/decomposition, and this salt is thenisolated by a known technique such as precipitation or filtration. Morespecifically, for example, the reaction mass is added to a dilutedaqueous hydrochloric acid solution containing stannous chloride todissolve 4,6-diaminoresorcin hydrochloride. In succession, the resultingsolution is filtered to remove the catalyst, and then the solvent isdistilled off under reduced pressure. Alternatively, the filtratedsolution is mixed with concentrated hydrochloric acid to depositcrystals, followed by filtration. When the aqueous hydrochloric acidsolution is used as the solvent, 4,6-diaminoresorcin hydrochloride isalready formed in the reduction reaction mass, and hence the steps ofthe salt-forming and the dissolving are not necessary. When phosphoricacid or sulfuric acid is used as the mineral acid and the4,6-diaminoresorcin mineral acid salt is deposited, the salt isdissolved in the form of 4,6-diaminoresorcin hydrochloride bysalt-exchanging, and crystals are then deposited in the similar manneras above.

[0081] An obtained 4,6-diaminoresorcin dimineral acid salt can befurther purified by a technique such as recrystallization. concretely,for example, after crude 4,6-diaminoresorcin dimineral acid salt isdissolved in water including stannous chloride, activated carbon isadded thereto, followed by treatment. Next, the activated carbon isremoved by filtration, and concentrated hydrochloric acid is then addedthereto for crystallization.

[0082] In order to obtain a PBO by the use of the thus obtained4,6-diaminoresorcin (E), a known polymerization method can be employed.For example, the PBO can be obtained by dissolving the4,6-diaminoresorcin dimineral acid salt in polyphosphoric acid, heatingthe resulting solution under reduced pressure to remove hydrochloricacid, adding a required amount of diphosphorus pentoxide, further addingaromatic dicarboxylic acid in a nearly equimolar amount to4,6-diaminoresorcin, and then stirring the mixture under heat. Examplesof the usable aromatic dicarboxylic acid include terephthalic acid,isophthalic acid, 4,4′-bis(benzoic acid), 4,4′-oxybis(benzoic acid) and2,6-naphthalene dicarboxylic acid.

[0083] The present invention will be described in more detail withreference to the following examples, by which the present invention isnot limited.

EXAMPLE 1 (Sulfonation step R1)

[0084] 100 g of 30 wt % fuming sulfuric acid (SO₃ concentration=87.1%,the amount of free SO₃=3.75 mols per mol of resorcin) were cooled withice, 11.0 g (0.1 mol) of resorcin were slowly added thereto. Afterward,the mixture was heated to 90° C. to give a dark-red homogeneous solutionof a reaction mass. According to the analysis of liquid chromatography(hereinafter abbreviated to “HPLC”), any peaks of resorcin and resorcin4,6-disulfonate were not confirmed, and the production ratio of resorcin2,4,6-trisulfonate was 99.8 mol %.

Conditions for HPLC Analysis

[0085] Column: YMC-312A (ODS)

[0086] Mobile phase: Acetonitrile:water:PIC=1000:2000:10

[0087] PIC=Tetrabutyl ammonium hydroxide

[0088] Flow rate: 1 ml/min

[0089] Detection wavelength: 254 nm

[0090] Thermostat layer: 40° C.

EXAMPLE 2 (Sulfonation step R1)

[0091] 100 g of 24 wt % fuming sulfuric acid (SO₃ concentration=86.0%,the amount of free SO₃=3 mols per mol of resorcin) were cooled with ice,and 11.0 g (0.1 mol) of resorcin were slowly added thereto. Afterward,the mixture was heated to 50° C. to give a dark-red homogeneous solutionof a reaction mass. According to the analysis of HPLC, the productionratio of resorcin 4,6-disulfonate was 0.6 mol %, and that of resorcin2,4,6-trisulfonate was 99.3 mol %.

EXAMPLE 3 (Sulfonation step R1)

[0092] 100 g of 16 wt % fuming sulfuric acid (SO₃ concentration=84.6%,the amount of free S₃=2 mols per mol of resorcin) were cooled with ice,and 11.0 g (0.1 mol) of resorcin were slowly added thereto. Afterward,the mixture was heated to 90° C., so that a reaction mass was obtainedin the state of an orange-colored viscous slurry containing a slightamount of a solid. According to the analysis of HPLC, the productionratio of resorcin 4,6-disulfonate was 9.5 mol %, and that of resorcin2,4,6-trisulfonate was 90.2 mol %. The reaction mass was further heatedto 130° C. to obtain a red homogeneous solution, but after reaction for30 minutes, the production ratio of resorcin 4,6-disulfonate was 13 mol%, and that of resorcin 2,4,6-trisulfonate was 87 mol %.

EXAMPLE 4 (Sulfonation step R1)

[0093] 100 g of 100 wt % sulfuric acid (SO₃ concentration=81.6%) werecooled with ice, and 11.0 g (0.1 mol) of resorcin were slowly addedthereto. Afterward, the mixture was heated to 90° C., so that a reactionmass was obtained in the state of a light pink slurry. According to theanalysis of HPLC, the production ratio of resorcin 4,6-disulfonate was93 mol %, and that of resorcin 2,4,6-trisulfonate was 6.5 mol %. Thereaction mass was further heated to 130° C., but no dissolution ofcrystals was observed, and the reaction mass remained in the form of thelight pink slurry. After reaction for 60 minutes, the production ratioof resorcin 4,6-disulfonate was 79 mol %, and that of resorcin2,4,6-trisulfonate was 21 mol %.

EXAMPLE 5 (Sulfonation step R1)

[0094] 100 g of 95 wt % sulfuric acid (SO₃ concentration=77.6%) werecooled with ice, and 11.0 g (0.1 mol) of resorcin was slowly addedthereto. Afterward, the mixture was heated to 50° C., so that a reactionmass was obtained in the state of a white slurry. According to theanalysis of HPLC, the production ratio of resorcin 4,6-disulfonate was88 mol %, and that of resorcin 2,4,6-trisulfonate was 12 mol %.

EXAMPLE 6 (sulfonation step R1)

[0095] 200 g of 95 wt % sulfuric acid (SO₃ concentration=77.6%) werecooled with ice, and 11.0 g (0.1 mol) of resorcin was slowly addedthereto. Afterward, the mixture was heated to 50° C., so that a reactionmass was obtained in the state of a white slurry. According to theanalysis of HPLC, the production ratio of resorcin 4,6-disulfonate was83 mol %, and that of resorcin 2,4,6-trisulfonate was 17 mol %.

EXAMPLE 7 (Nitration step R2)

[0096] In the same manner as in Example 1, 5.5 g (0.05 mol) of resorcinwere added to 50 g of 30 wt % fuming sulfuric acid, and the resultantsulfonated mass was then cooled with ice. Afterward, 10.5 g (0.1 mol) of60 wt % nitric acid were added dropwise thereto, so that heat wasvigorously generated and the reaction mass became a yellow-brown slurry.

[0097] This nitrated mass was added to 100 g of ice, and 27.7 g of a 49%aqueous sodium hydroxide solution were then added dropwise thereto underice cooling, so that yellow-white crystals were deposited to form aslurry. The slurry was filtered, and the resultant filter cake was thenwashed with 100 g of ethanol to obtain 9.44 g of a mixture of 2-sulfonicacid-4, 6-dinitroresorcin sodium salt and sodium sulfate.

[0098] 5.04 g of the above mixture were added to 200 g of a mixedsolution of water and ethanol in a ratio of 20:80. After the mixture wassludged and filtered under heat at 80° C., the filtrate was cooled byallowing it to stand at room temperature, so that the deposition ofcrystals was observed. Next, the crystals were collected by filtrationto obtain 1.07 g of yellow crystals of 2-sulfonicacid-4,6-dinitroresorcin sodium salt.

[0099] 1.07 g of this compound were dissolved in 25 g of water, and theresultant solution was passed through a column filled with 20 ml of anion exchange resin (MD-S1368) and then washed with 30 g of water. Thissolution was evaporated by an evaporator, dried under nitrogen, washedwith ethanol, and then filtered to obtain 130 mg of crystals of2-sulfonic acid-4,6-dinitroresorcin.

[0100] The ¹³C-NMR spectrum of 2-sulfonic acid-4,6-dinitroresorcinsynthesized in this example showed the following absorptions, and theseabsorptions were ascribed to carbons a to d in the following structuralformula, respectively. δ = 119.4 ppm a (aromatic carbon substituted byNO₂) δ = 125.2 ppm b (aromatic carbon substituted by SO₃H) δ = 128.9 ppmc (aromatic carbon to which hydrogen was bonded) δ = 155.0 ppm d(aromatic carbon substituted by OH)

[0101] Furthermore, according to the measurement of aninfrared-absorbing spectrum, the following distinctive absorption bandswere observed. 1588 cm⁻¹ NO₂ (absorbing band due to asymmetricstretching vibration) 1363 cm⁻¹ NO₂ (absorbing band due to symmetricstretching vibration) 1332 cm⁻¹ SO₂ (absorbing band due to asymmetricstretching vibration) 1154 cm⁻¹ SO₂ (absorbing band due to symmetricstretching vibration)

EXAMPLE 8 (Nitration step R2)

[0102] 4.12 g of 9.44 g of a mixture of 2-sulfonicacid-4,6-dinitroresorcin sodium salt obtained in Example 7 and sodiumsulfate were added to 100 g of a mixed solution of water and ethanol ina ratio of 20:80. After the mixture was sludged and filtered under heatat 80° C., the filtrate was cooled by allowing it to stand at roomtemperature, so that the deposition of crystals was observed. Thecrystals were collected by filtration and then air-dried under nitrogento obtain 1.18 g of yellow crystals of 2-sulfonicacid-4,6-dinitroresorcin sodium salt.

[0103] The ¹³C-NMR spectrum of 2-sulfonic acid-4,6-dinitroresorcinsodium salt synthesized in this example showed the followingabsorptions, and these absorptions were ascribed to carbons a to d inthe following structural formula, respectively. δ = 119.4 ppm a(aromatic carbon substituted by NO₂) δ = 125.2 ppm b (aromatic carbonsubstituted by SO₃H) δ = 128.9 ppm c (aromatic carbon to which hydrogenwas bonded) δ = 155.0 ppm d (aromatic carbon substituted by OH)

[0104] Furthermore, according to the measurement of aninfrared-absorbing spectrum, the following distinctive absorption bandswere observed.

[0105] 1588 cm⁻¹ NO₂ (absorbing band due to asymmetric stretchingvibration)

[0106] 1363 cm⁻¹ NO₂ (absorbing band due to symmetric stretchingvibration)

[0107] 1332 cm⁻¹ SO₂ (absorbing band due to asymmetric stretchingvibration)

[0108] 1154 cm⁻¹ SO₂ (absorbing band due to symmetric stretchingvibration)

Elementary Analysis Values (%) of C₆H₃N₂O₉SNa

[0109] Element C H N S Na Calcd. 23.86 1.00 9.27 10.59 7.61 Found 23.680.99 9.24 10.80 7.89

EXAMPLE 9 (Hydrolysis step R3)

[0110] 15.1 g (0.05 mol) of 2-sulfonic acid-4,6-dinitroresorcin sodiumsalt were added to 250 g of a 20 wt % aqueous sulfuric acid solution,and the resultant solution was then heated at 100° C. for 7 hours,during which the gradual deposition of crystals was observed. After thereaction mass was cooled to room temperature, it was collected byfiltration to obtain 8.95 g of yellow-white crystals. The crystals wererecrystallized from 500 g of ethanol, and then air-dried under nitrogento obtain 7.6 g of purified 4,6-dinitroresorcin.

EXAMPLE 10 (R1 to R3 in sequence)

[0111] 5.5 g (0.05 mol) of resorcin were slowly added to 50 g of 30%fuming sulfuric acid, and the reaction mass was then heated to 90° C. tothereby become a dark-red solution. The production of resorcin2,4,6-trisulfonate was confirmed by HPLC analysis. The sulfonated masswas cooled with ice, and 10.5 g (0.1 mol) of 60% nitric acid was thenadded dropwise thereto, so that heat was vigorously generated and thereaction mass became a yellow-brown slurry.

[0112] The nitrated mass was added to 100 g of ice, and then heated to100° C. to carry out hydrolysis, so that the gradual deposition ofcrystals was observed. The crystals were collected by filtration andair-dried under nitrogen to obtain 8.02 g (yield=80.3% based onresorcin) of 4,6-dinitroresorcin.

EXAMPLE 11 (Steps R1 to R4)

[0113] 55 g (0.5 mol) of resorcin were slowly added to 500 g of 30 wt %fuming sulfuric acid, and the mixture was heated to 90° C., so that thereaction mass became a dark-red solution. The production of resorcin2,4,6-trisulfonate was confirmed by HPLC analysis.

[0114] The sulfonated mass was cooled with ice, and 105 g (1.0 mol) of60 wt % nitric acid was added dropwise thereto, so that heat wasvigorously generated and the reaction mass became a yellow-brown slurry.This nitrated mass was added to 1,095 g of ice, and then heated to 100°C. to carry out hydrolysis, so that the gradual deposition of crystalswas observed. The crystals were collected by filtration, sludged with500 g of water, and then air-dried under nitrogen to obtain 81.2 g(yield=81.2%) of crude 4,6-dinitroresorcin.

[0115] 30 g of crude 4,6-dinitroresorcin were recrystallized in 1,500 gof ethanol to obtain 24.1 g of purified 4,6-dinitroresorcin. Next, 4.0 gof this purified 4,6-dinitroresorcin were added to methanol, and 0.0396g of 5% palladium carbon (a 50% wet product) was then added thereto,followed by hydrogenation at 60° C. under an average hydrogen pressureof 0.8 MPaG. The reaction mass was poured into a 5% aqueous hydrochloricacid solution containing 6,000 ppm of stannous chloride, and thenfiltered to remove the catalyst.

[0116] Afterward, analysis was carried out by HPLC, and it was confirmedthat desired 4,6-diaminoresorcin was produced in a yield of 96.2 mol %.The solvent was removed from the filtrate by an evaporator to obtain thecrystals of crude 4,6-dinitroresorcin. The crystals were dissolved in21.3 g of water containing 0.32 g of stannous chloride, and 0.2 g ofactivated carbon was added to the solution. Thereafter, the solution wasstirred for 30 minutes and then filtered to remove the activated carbon.When 16.0 g of 36% hydrochloric acid were gradually added dropwise tothe filtrate, the gradual deposition of crystals was observed. Thecrystals were collected by filtration and then dried at 50° C. underreduced pressure to obtain 3.03 g (yield=46.4%) of 4,6-diaminoresorcindihydrochloride.

EXAMPLE 12

[0117]10 g of purified 4,6-dinitorresorcin obtained in Example 11 wereadded to 73.4 g of a 5.2% aqueous hydrochloric acid solution. To thesolution was added 0.9 g of 2% platinum carbon (a 56% water-containingproduct), and hydrogenation was then carried out at 60° C. under ahydrogen pressure of 0.8 MPa. After the reaction mass was filtered toremove the catalyst, 0.75 g of activated carbon was added to thefiltrate. Thereafter, the filtrate was stirred for 30 minutes and thenfiltered to remove the activated carbon. When 23 g of hydrogen chloridewere added to the filtrate, the gradual deposition of crystals wasobserved. The crystals were collected by filtration and then dried underreduced pressure to obtain 10.2 g (yield=95.7%) of 4,6-diaminoresorcindihydrochloride.

EXAMPLE 13

[0118]32 g (0.16 mol) of 4,6-dinitroresorcin produced in the same manneras in Example 10 were added to 1,440 g of ethyl acetate, and the mixturewas then heated to 80° C. to become a homogeneous solution. Next, 200 gof hot water at 80° C. were added to the mixture, and a pH electrode wasthen immersed into the solution. Afterward, a 49% aqueous sodiumhydroxide solution was added dropwise thereto to adjust a pH of thesystem to 4.3, and the solution was then stirred at the same temperaturefor one hour.

[0119] The stirring was terminated, and the solution-was then allowed tostand for one hour. Thereafter, water was discharged through the bottomof the flask. 200 g of hot water was-added to the remaining4,6-dinitroresorcin ethyl acetate solution in the flask, followed bystirring at 80° C. for one hour. After the stirring was stopped, thesolution was allowed to stand for one hour and the resultant liquidphases were then separated. This operation was further repeated twice.

[0120] The remaining 4,6-dinitroresorcin ethyl acetate solution in theflask was gradually cooled to 20° C. to deposit yellow crystals. Thissolution was suction-filtered, washed with hot water, and then dried at30° C., thereby obtaining 20.8 g of 4,6-dinitroresorcin.

[0121] 20 g of the thus obtained 4,6-dinitroresorcin, 0.4 g of 2%platinum carbon and 146.7 g of a 5.2% aqueous hydrochloric acid solutionwere placed in a 0.3-liter autoclave made of tantalum, and hydrogenationreaction was then carried out at a reaction temperature of 60° C. and astirring speed of 1,000 rpm under a hydrogen pressure of 0.78 MPa. Thereaction was completed in a reaction time of 95 minutes. Thereafter, thecatalyst was filtered out, whereby a colorless transparent reactionsolution was obtained. The reaction results in this case were such thatthe conversion rate of 4,6-dinitroresorcin was 100% and the yield of4,6-diaminoresorcin dihydrochloride was 98%.

[0122] In succession, 35 g of hydrogen chloride were blown into theabove reaction solution to deposit white crystals. This solution wasfiltered, washed with acetone, and then dried at 30° C. to obtain 20.4 gof white 4,6-diaminoresorcin dihydrochloride.

Example 14

[0123]32 g of 4,6-dinitroresorcin produced in the same manner as inExample 10 were added to 128 g of methanol, and the resulting mixturewas then heated to 50° C. To the obtained slurry solution was added a49% aqueous sodium hydroxide solution to adjust the pH of the solutionto 4.3. After stirred at the same temperature for one hour, the solutionwas cooled to 20° C. This treated solution was filtered, washed withmethanol and then water, and dried at 30° C. to obtain 31.2 g of4,6-dinitroresorcin. 20 g of the thus obtained 4,6-dinitroresorcin, 0.4g of 2% platinum carbon and 146.7 g of a 5.2% aqueous hydrochloric acidsolution were placed in a 0.3-liter autoclave made of tantalum, andhydrogenation reaction was then carried out at a reaction temperature of60° C. and a stirring speed of 1,000 rpm under a hydrogen pressure of0.78 MPa. The reaction was completed in a reaction time of 100 minutes.Thereafter, the catalyst was filtered out to obtain a reaction solution.The reaction results in this case were such that the conversion rate of4,6-dinitroresorcin was 100% and the yield of 4,6-diaminoresorcindihydrochloride was 97.5%.

EXAMPLE 15

[0124] 50 g of 4,6-dinitroresorcin produced in the same manner as-inExample 10 were added to 570 g of water, and 40.8 g of a 49% aqueoussodium hydroxide solution were added to the mixture at a temperatures of20 to 30° C. to prepare a homogeneous solution. A 36% aqueoushydrochloric acid solution was added dropwise to the above homogenoussolution to adjust the pH of the solution to 4.3, so that the materialbecame a slurry state. This slurry was filtered, washed with water, andthen dried at 30° C. to obtain 49 g of 4,6-dinitroresorcin.

[0125] 20 g of the thus obtained 4,6-dinitroresorcin, 0.4 g of 2%platinum carbon and 146.7 g of a 5.2% aqueous hydrochloric acid solutionwere placed in a 0.3-liter autoclave made of tantalum, and hydrogenationreaction was then carried out at a reaction temperature of 60° C. and astirring speed of 1,000 rpm under a hydrogen pressure of 0.78 MPa. Thereaction was completed in a reaction time of 100 minutes. Thereafter,the catalyst was filtered out to obtain a reaction solution. Thereaction results in this case were such that the conversion rate of4,6-dinitroresorcin was 100% and the yield of 4,6-diaminoresorcindihydrochloride was 97.6%.

[0126] EXAMPLE 16 (Steps R1 to R4 and polymerization of PBO)

[0127] 110.0 g (1 mol) of resorcin were slowly added to 1,000 g of 30%fuming sulfuric acid, and the mixture was then heated up to 50° C., sothat a reaction mass became a dark-red solution. According to HPLCanalysis, the production of resorcin 2,4,6-trisulfonate was confirmed.

[0128] The sulfonated mass was cooled with ice, and 210 g (2 mol) of 60wt % nitric acid were added dropwise thereto, so that heat wasvigorously generated and the reaction mass became a yellow-brown slurry.

[0129] The nitrated mass was poured into 2,200 g of ice, followed byhydrolysis at 100° C. for 7 hours, so that the gradual deposition ofcrystals was observed. The solution was cooled to room temperature andthen filtered, and the obtained crystals were washed with ethanol,filtered and air-dried under nitrogen to obtain 130.5 g (yield=65.2%) of4,6-dinitroresorcin.

[0130] This 4,6-dinitroresorcin was placed in an autoclave, and 660 mlof methanol and 2.7 g of 5% Pd/C were further added to the autoclave.Here, hydrogenation reaction was carried out at 60° C. under a hydrogenpressure of 0.78 MPa. When the absorption of hydrogen was no longerobserved, the reaction mass was cooled to room temperature, and thenpoured into 760 g of a 5% aqueous hydrochloric acid solution to dissolvethe product therein. After the mixture was filtered to remove thecatalyst, the solvent was removed therefrom by an evaporator to obtain133.6 g (yield=62.7%) of crude 4,6-diaminoresorcin dihydrochloride.

[0131] This crude 4,6-diaminoresorcin dihydrochloride was dissolved-in670 g of water containing 10 g of stannous chloride, and 11 g ofactivated carbon were added for a discoloration treatment. The mixturewas filtered to remove the activated carbon, and 510 g of 36%hydrochloric acid were added dropwise to the filtrate to depositcrystals, which were then filtered out to obtain 106.6 g (yield=50.01%)of purified 4,6-diaminoresorcin dihydrochloride. 40% by weight of 85%H₃P₄and 60 wt % of 115% polyphosphoric acid were mixed with each otherto prepare a polyphosphoric acid solution (a PPA solution) containing74.9% of P₂O₅. Then, 22.82 g (0.11 mol) of the above-described purified4,6-diaminoresorcin dihydrochloride were added to 88.6 g of the PPAsolution, and the solution was stirred and then heated at 50 to 80° C.for about 20 hours under reduced pressure to remove hydrochloric acidtherefrom. To this mixture were added 17.96 g (0.11 mol) of terephthalicacid, and then 61.2 g of P₂O₅were added thereto to adjust the content ofP₂O₅in the mixture to 87.2 wt %. This mixture was stirred at 100° C. for15 hours under argon stream. Then, while the mixed solution wasvigorously stirred, its temperature was elevated up to 178° C. within 40minutes, and at this temperature, the solution was further stirred for25 hours. Next, the temperature of the solution was elevated up to 185°C. within one hour, and at this temperature, the solution was allowed toreact for 25 hours to obtain a reaction solution containingpoly(p-phenylenebenzobisoxazole) (PBO). This reaction solution wasprecipitated in water, and fully washed with water to prepare a PBOpowder from which the PPA was completely removed. The intrinsicviscosity of the obtained PBO was 25.2 dl/g (30° C., methanesulfonicacid).

What is claimed is:
 1. A production method of resorcin2,4,6-trisulfonate which comprises the step of bringing resorcin intocontact with a sulfonating agent.
 2. The production method of resorcin2,4,6-trisulfonate according to claim 1, wherein fuming sulfuric acid isused as the sulfonating agent.
 3. The production method of resorcin2,4,6-trisulfonate according to claim 2, wherein fuming sulfuric acid tobe used contains 3 mols or more of free SO₃per mol of resorcin.
 4. Aproduction method of 2-sulfonic acid-4,6-dinitroresorcin which comprisesthe step of nitrating resorcin 2,4, 6-trisulfonate.
 5. The productionmethod of 2-sulfonic acid-4,6-dinitroresorcin according to claim 4,wherein the nitration is carried out in sulfuric acid or a fumingsulfuric acid solvent.
 6. A production method of 2-sulfonicacid-4,6-dinitroresorcin which comprises the following steps: (1) afirst step of producing resorcin 2,4,6-trisulfonate by bringing resorcininto contact with a sulfonating agent, and (2) a second step ofproducing 2-sulfonic acid-4,6-dinitroresorcin by bringing resorcin2,4,6-trisulfonate into contact with a nitrating agent.
 7. A productionmethod of 4,6-dinitroresorcin which comprises the step of hydrolyzing2-sulfonic acid-4, 6-dinitroresorcin.
 8. The production method of4,6-dinitroresorcin according to claim 7, wherein the hydrolysis iscarried out in water or an aqueous mineral acid solution.
 9. Theproduction method of 4,6-dinitroresorcin according to claim 8, whereinsulfuric acid is used as the mineral acid.
 10. A production method of4,6-dinitroresorcin which comprises the following steps: (1) a firststep of producing resorcin 2,4,6-trisulfonate by bringing resorcin intocontact with a sulfonating agent, (2) a second step of producing2-sulfonic acid-4,6-dinitroresorcin by bringing resorcin2,4,6-trisulfonate into contact with a nitrating agent, and (3) a thirdstep of producing 4,6-dinitroresorcin by hydrolyzing 2-sulfonicacid-4,6-dinitroresorcin.
 11. A production method of 4,6-diaminoresorcinwhich comprises the following steps: (1) a first step of producingresorcin 2,4,6-trisulfonate by bringing resorcin into contact with asulfonating agent, (2) a second step of producing 2-sulfonicacid-4,6-dinitroresorcin by bringing resorcin 2,4,6-trisulfonate intocontact with a nitrating agent, (3) a third step of producing4,6-dinitroresorcin by hydrolyzing 2-sulfonic acid-4,6-dinitroresorcin,and (4) a fourth step of producing 4,6-diaminoresorcin by reducing4,6-dinitroresorcin.
 12. A production method of polybenzobisoxazolewhich comprises the steps of hydrolyzing 2-sulfonicacid-4,6-dinitroresorcin, followed by reducing to obtain4,6-diaminoresorcin, and then reacting the thus obtained4,6-diaminoresorcin with aromatic dicarboxylic acid.
 13. 2-Sulfonicacid-4,6-dinitroresorcin represented by the following formula and saltsthereof:

wherein M is hydrogen, an alkali metal or an alkaline earth metal, and nis 1 or
 2. 14. A production method of 4,6-diaminoresorcin whichcomprises: (1) a first step of producing 4,6-dinitroresorcin byhydrolyzing 2-sulfonic acid-4,6-dinitroresorcin, and (2) a second stepof producing 4,6-diaminoresorcin by reducing 4,6-dinitroresorcin. 15.The production method of 4,6-diaminoresorcin according to claim 14,wherein 2-sulfonic acid-4,6-dinitroresorcin is obtained by the followingsteps: (1) a first step of producing resorcin 2,4,6-trisulfonate bybringing resorcin into contact with a sulfonating agent, and (2) asecond step of producing 2-sulfonic acid-4,6-dinitroresorcin by bringingresorcin 2,4,6-trisulfonate into contact with a nitrating agent.
 16. Theproduction method of 4,6-diaminoresorcin according to claim 14, whereinin the second step, 4,6-dinitroresorcin is reduced in an aqueous mineralacid solution.
 17. The production method of 4,6-diaminoresorcinaccording to claim 16, wherein hydrochloric acid is used as the mineralacid.
 18. The production method of 4,6-diaminoresorcin according toclaim 14 which comprises the steps of dissolving or suspending4,6-dinitroresorcin in a solvent, adjusting the pH of the suspension ina range of 4 to 5 to obtain 4,6-dinitroresorcin, and then reducing thethus obtained 4,6-dinitroresorcin.